A coordinate input device is an efficient means in the field of digital techniques and particularly as a means to input information into a computer. Various types of coordinate inputting devices are known. For example, those disclosed in U.S. Pat. No. 4,566,001, which are located in front of a display device, permitting an input operation according to the content of the display, or those disclosed in U.S. Pat. No. 4,504,700, for which an input operation can be effected by the coordinating input device alone. Due to the ease of learning the input operation, there is a growing trend toward the use of input devices which provide an input according to the content of a display. These devices include various sorts of detecting means such as a coordinate input device as disclosed e.g. in U.S. Pat. No. 4,423,299, having electrical contacts, a coordinate input device as disclosed e.g. in U.S. Pat. No. 4,238,792, having a light pen, a coordinate input device as disclosed e.g. in U.S. Pat. No. 3,916,099, having detecting means for detecting mechanical vibration, etc. No matter what detecting means are used, where they are used for a digital computer, the values of the coordinate data for the ordinate and the abscissa are outputted time sequentially. When the relation between the coordinate input device and the computer is considered, it is usual that the computer's processing capabilities are required for almost all processings. An example which tries to deal with this problem is disclosed in well known U.S. Pat. No. 3,875,403. The detecting means for this coordinate input device is constructed of photoelectric switches which recognize the interruption of a plurality of beams between light emitting and receiving devices. Recently the properties of these types of coordinate input devices have been evaluated to be excellent. In addition, the industrial infrastructure for supplying semiconductor light emitting and receiving devices is well organized. The demands for and on such devices have increased greatly both from the point of view of their supply and from the point of view of their characteristics.
The prior art techniques will be explained below, taking such a coordinate input device as an example.
These types of optical coordinate detecting devices contain a plurality of pairs of light sources and corresponding light sensitive elements with a predetermined frequency (spacing). Light sources are driven one after another, depending on the counter value outputted by a counting circuit; when the light path is interrupted due to a coordinate input operation and the corresponding light sensitive element does not receive any light, a detection signal is outputted. The counter value corresponding to this detection signal is outputted as an input coordinate. Further, devices effecting the coordinate detection in X - Y coordinates contain a plurality of pairs of light sources and corresponding light sensitive elements in the directions of the X and the Y axes.
In these devices, where a plurality of light paths emitted by these light sources are interrupted at the same time and a plurality of light sensitive elements do not receive any light so that detection signals are outputted successively in the order of their drive, it is desirable that the average value of the inputted coordinates is calculated as their central position.
Techniques for calculating the average value of inputted coordinates are disclosed in JP-A-60-86417. According to these techniques all the inputted coordinates detected successively are added by means of an adder and the average value is calculated by dividing the sum thus obtained by the number of the successively inputted coordinates.
Further, among this kind of device, in an optical coordinate detecting device, every time one scan is terminated, an undetection code, which indicates that there is no inputted coordinate (or no coordinate is inputted), is outputted to a host computer. Then scanning is again started by a signal coming from the host computer.
Furthermore, among this kind of device, the host computer judges in which detection area the inputted coordinate is and a menu operation corresponding to that detection area is carried out.